In the navigation of aircraft over a prescribed route, contour maps have been conventionally employed to provide an indication of the terrain over which the aircraft is flying. This information, together with instrument readings and visual observation of the terrain from the cockpit, enables the pilot to determine altitude and course of the aircraft as it travels along its flight path. For low altitude flying, such as might be experienced in a helicopter, an instantaneous picture of the details of the terrain over which the aircraft is flying is of paramount importance in guiding the aircraft, especially where the contour of the terrain changes rapidly and contains obstacles to the flight of the aircraft.
In copending application Ser. No. 641,179, filed Aug. 15, 1984, which is a continuation of copending application Ser. No. 224,742, filed Jan. 13, 1981, now abandoned, by Paul B. Beckwith, Jr. entitled "Digital Map Generator and Display System", assigned to the assignee of the present application, there is described a system for effecting the dynamic display of terrain data which is stored in digital format and which may be viewed on a cockpit cathode ray tube display in the form of a moving map of the terrain over which the aircraft is flying, offering the pilot an advanced navigational tool not previously provided by conventional terrain mapping schemes.
The system described in that application operates so as to automatically orient the moving map, under the control of the aircraft's navigational computer system, to the instantaneous position of the aircraft with a heading-up disposition. Within this system there is employed a scene memory which stores terrain data and which is selectively accessed to generate the map display. The stored terrain data encompasses a number of definitive aspects of the terrain including, inter alia, both elevation and cultural information, so that the system is capable of providing a maximum of information to assist the pilot in navigating and controlling the aircraft.
Now, although the generation of a plan view map of the terrain over which the aircraft is flying greatly assists the pilot, he still relies on as many information sources as possible, including instrument readings and his own view from the cockpit. Unfortunately, in restricted visibility conditions, such as nighttime flying, poor weather, smoke, etc. the pilot's view of what lies ahead of the aircraft may provide very little, if any, information. Ideally, the pilot would prefer to always see the terrain ahead of the aircraft as it appears in daylight, high visibility conditions.